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The radius of curvature of a thin plano-convex lens is 10 cm (curved surface) and the refractive index is 1.5. If the plane surface is silvered, then it behaves like a concave mirror of focal length

1. 10 cm
2. 15 cm
3. 20 cm
4. 5 cm

Correct answer: 20 cm

Solution

When the plane surface of the plano-convex lens is silvered, it acts as a concave mirror with an effective focal length determined by the lens-mirror combination. Using the mirror-lens formula, the effective focal length is calculated as 20 cm.

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